A polynomial preserving recovery technique is applied to an
over-penalized symmetric interior penalty method. The
discontinuous Galerkin solution values are used to recover the
gradient and to further construct an a posteriori error estimator in
the energy norm. In addition, for uniform triangular meshes and
mildly structured meshes satisfying the $\epsilon$-$\sigma$
condition, the method for the linear element is superconvergent
under the regular pattern and under the chevron pattern, while it is
superconvergent for the quadratic element under the regular pattern.